The present invention relates to an image forming apparatus of the type including a plurality of process means for forming a visible image on an image carrier which is adapted to carry an electrophotostatic latent image, transferring the visible image to a transfer material, and cleaning the image carrier after the image transfer. More particularly, the present invention is concerned with an electrophotographic copier, printer, facsimile apparatus and other image forming apparatuses having at least one image forming unit and an image carrier which are individually removably mounted on the apparatus, a unit life sensor for sensing the end of the life of the image forming unit, and an image carrier life sensor for sensing the end of the life of the image carrier.
An image forming apparatus of the type described has been implemented as a printer, facsimile apparatus or the like and proposed in a variety of configurations, as disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 61-118770 by way of example. In this type of apparatus, at least one of various process means such as a charging device, exposing device, developing device, transferring device, cleaning device and discharging device is constructed into an image forming unit which is independent of an image carrier. This independent unit and the image carrier are individually removably mounted on the apparatus, so that any one of them may be replaced with a new one when its life expires. Also known in the art is an image forming apparatus in which the image carrier is combined with at least one of the process means to constitute an image forming unit which is removable from the the apparatus. In this kind of apparatus, when the life of the process means or that of the image carrier of the image forming unit expires, the entire image forming unit is replaced. This scheme, however, tends to force a user to bear an excessive burden in the economic aspect. Specifically, in parallel with the recent progress in technology, the life of, for example, the image carrier which is constituted by a photoconductive element is becoming longer than those of the developing device, cleaning device and other process means. In the case that such an image carrier and process means such as the developing device or cleaning device are constructed into an image forming unit, when the life of the process unit expires, even the image carrier which is still usable has to be discarded simply wastefully. The first-described type of apparatus in which the image forming unit and the image carrier are independent of each other is advantageous in that the image forming unit can be replaced independently of the image carrier and, therefore, the image carrier can be used til the end of its life.
As will be understood from the above, allowing the image carrier and the image forming unit to be replaced independently of each other is desirable from the economical standpoint. However, replacing them independently of each other results in the need for frequent replacement which would be troublesome for an operator.